ESR1 and obesity due to melanocortin 4 receptor deficiency: Obesity, defined as an excessive body fat, has been associated both with a higher risk of developing BC, particularly in postmenopausal women, and with worse disease outcome for women of all ages [105], and elevated waist-to-hip ratio (WHR) was as a predictor of BC mortality in estrogen receptor (ER)-positive postmenopausal women [106].